1. Field of the Invention
The present invention generally relates to the field of high-pressure fuel pumps for use with internal combustion engines. More particularly, the present invention is directed to common-rail fuel pumps of the type having reciprocating plungers for periodically delivering fuel at high pressure to an accumulator for fuel injection. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
2. Description of the Related Art
Fuel pumps for use with fuel injected internal combustion engines are widely known in the art. While the earliest of such pumps delivered charges of fuel directly to a plurality of fuel injectors, more recent developments have focused on common-rail fuel-delivery systems which operate at higher fuel pressures. One such common-rail fuel pump is disclosed in co-pending U.S. patent application Ser. No. 08/883,448 which was filed on Jun. 26, 1997. The contents of this application are hereby incorporated by reference to provide additional details regarding high-pressure fuel pumps and their associated fuel injection systems.
Related art fuel pumps such as those disclosed in the incorporated application are typically designed to operate at fuel pressures of about 1,000 bar or less. While such pumps presently operate quite effectively, they are likely to become deficient in the future as governmentally imposed emission control standards become more demanding. This is because, in order to meet the stricter emission standards expected in the future, internal combustion engine manufacturers have been requiring higher and higher fuel pressures from fuel pumps used therewith. Thus, while state of the art fuel pumps produce fuel pressures up to about 1,000 bar, it is expected that fuel pressures above about 2,000 bar will become commonplace in the near future.
This increase in fuel-pressure may be achieved by either modifying conventional pumps or by developing new pump designs. For example, it may be possible to modify the various components of related art high-pressure fuel pumps in order to increase the pressure of the fuel pumped from such conventional pumps. However, fuel pumps of the related art inherently possess a number of limitations which severely limit the amount by which fuel-pressure can be increased. For example, the pressure of fuel pumped from related art fuel pumps can be increased to a small extent merely by reducing the diameter of the pumping plungers used therein (e.g., from about 0.270 inches to about 0.210 inches). Such a modification can be expected to increase the fuel-pressure of the related art pumps from a maximum of about 1,000 bar to a maximum of about 2,000 bar.
Further decreases in the diameter of the pumping plungers, however, are simply neither practical nor economical for a number of reasons. For example, the cost of manufacturing pumps increases radically as the size of the pumping plungers decreases. Moreover, fuel leakage losses increase as the size of the pumping plungers decreases because as plunger size decreases more plungers are necessary to maintain a given displacement. Other problems result from the low lubricity of some fuels, such as diesel fuel, and because of the high Hertzian stresses typically encountered within such pumps.
Another limitation associated with achieving fuel pressures in excess of 2,000 bar relates to the need for expensive high-pressure seals to seal the various components of such a pump. Generally speaking, redesigning existing fuel pumps to achieve still higher fuel pressures may lead to severe fuel leakage due to the size of various components and to the limitations of existing seals. This problem can be reduced by using higher quality seals throughout the pump. However, this is an expensive solution, especially if the use of high quality seals can be avoided altogether.
Accordingly, there remains a need in the art for a high-pressure fuel pump for use with internal combustion engines which is capable of delivering fuel at pressures in excess of 2,000 bar. Naturally, an ideal fuel pump capable of delivering such high fuel pressures will need to be both reliable and cost effective.
There is a further need in the art for improved methods of supplying high-pressure fuel to internal combustion engines which will reliably and inexpensively meet or exceed the fuel-pressure demands expected in the near future.